1. Field of the Invention
The present invention relates to a video cassette recorder, and more particularly to an audio playback system and method capable of preventing an occurrence of noise when a plurality of audio heads are switched.
2. Description of the Prior Art
In general VHS type video cassette recorders (VCRs), record and playback of video signals are achieved by a rotating head utilizing a drum, while record and playback of audio signals are achieved by a fixed head.
In conventional Hi-Fi VCRs, however, two audio dedicated heads are arranged on a drum and function to record audio signals on a VCR tape and play back therefrom alternately, when the drum rotates.
Now, an audio playback system for such conventional Hi-Fi VCRs will be described, in conjunction with FIG. 1.
FIG. 1 is a block diagram of the audio playback system used for the above-mentioned Hi-Fi VCRs. As shown in FIG. 1, the audio playback system comprises two audio heads 1 and 2 for playing back audio signals recorded on a VCR tape (not shown in FIG. 1) in a frequency modulation manner. Audio signals played back by audio heads 1 and 2 are amplified to predetermined levels by pre-amplifiers 3 and 4, respectively. The audio playback system also comprises filters 5 to 8 for separating audio signals from pre-amplifiers 3 and 4 into signals corresponding to left and right stereo channels and then filtering the separated signals to remove noise therefrom. Filters 5 and 7 are provided for processing the audio signal from the pre-amplifier 3, while filters 6 and 8 are provided for processing the audio signal from the pre-amplifier 4. To filters 5 to 8, demodulators 9 to 12 are connected, to demodulate signals from filters 5 to 8 into signals having original frequencies, respectively. The audio playback system also comprises switches 13 and 14 switched according to the level of a switching control signal SCP supplied externally to to combine audio signals modulated in demodulators 9 to 12 into two continuous audio signals one corresponding to the left channel and the other corresponding to the right channel. By digital/analog converters (D/A converters) 17 and 18, the combined digital audio signals are converted into original analog audio signals to be applied to playback output terminals 17 and 18 for left and right channels, respectively.
The operation of the conventional audio playback system will now be described.
Audio heads 1 and 2 play back frequency modulated audio signals recorded on the VCR tape, alternately. The played back audio signals which are weak in level are then amplified at predetermined amplifying levels by pre-amplifiers 3 and 4, respectively. The audio signal amplified by the pre-amplifier 3 is separated into left and right channel audio signals and then filtered by filters 5 and 7 to remove noise therefrom, respectively. On the other hand, the audio signal amplified by the pre-amplifier 4 is separated into left and right channel audio signals and then filtered by filters 6 and 8 to remove noise therefrom, respectively. Respective filtered audio signals from filters 5 to 8 are demodulated into digital signals having original frequencies, by demodulators 9 to 12.
Left channel audio signals demodulated by modulators 9 and 10 are received at fixed terminals b1 and c1 of the switch 13, respectively, to form a continuous signal. On the other hand, right channel audio signals demodulated by modulators 11 and 12 are received at fixed terminals b2 and c2 of the switch 14, respectively, to form a continuous signal. At this time, operations of switches 13 and 14 are controlled according to the level of a switching control signal SCP supplied externally. When a low level of switching control signal SCP is applied to switches 13 and 14, movable terminals a1 and a2 of switches 13 and 14 are connected to fixed terminals c1 and c2, respectively. Accordingly, digital audio signals from demodulators 10 and 12 are converted into original analog audio signals by D/A converters 15 and 16 and then applied to playback output terminals 17 and 18, respectively. On the other hand, when the switching control signal SCP has a high level, movable terminals a1 and a2 of switches 13 and 14 are connected to fixed terminals b1 and b2, respectively. Accordingly, digital audio signals from demodulators 9 and 11 are converted into original analog audio signals by D/A converters 15 and 16 and then applied to playback output terminals 17 and 18, respectively.
Thus, left channel audio signals from demodulators 9 and 10 are combined into a continuous signal by the switch 13, according to the level of external switching control signal SCP. In similar, right channel audio signals from demodulators 11 and 12 are combined into a continuous signal by the switch 14, according to the level of external switching control signal SCP.
In such a conventional audio playback system for Hi-Fi VCR, however, two audio heads arranged on the drum are operated alternately, to record continuously generated audio signals on a VCR tape and play them back alternately. Since these played back audio signals for the same channel are in a disconnected state from one another, they are combined into a continuous audio signal by a switch. At this time, a phase difference occurs between audio signals for the same channel played back by the two audio heads, so that noise always occurs at the point at which two played back audio signals are connected. The noise deteriorates the audio quality greatly.